diff --git a/lib/modules/auth/phone/PhoneAuthListener.js b/lib/modules/auth/phone/PhoneAuthListener.js
index 68bc78fb..f520638f 100644
--- a/lib/modules/auth/phone/PhoneAuthListener.js
+++ b/lib/modules/auth/phone/PhoneAuthListener.js
@@ -284,9 +284,9 @@ export default class PhoneAuthListener {
 
   on(
     event: string,
-    observer: () => PhoneAuthSnapshot,
-    errorCb?: () => PhoneAuthError,
-    successCb?: () => PhoneAuthSnapshot
+    observer: PhoneAuthSnapshot => void,
+    errorCb?: PhoneAuthError => void,
+    successCb?: PhoneAuthSnapshot => void
   ): this {
     if (!isString(event)) {
       throw new Error(
@@ -327,7 +327,7 @@ export default class PhoneAuthListener {
    * Promise .then proxy
    * @param fn
    */
-  then(fn: () => PhoneAuthSnapshot) {
+  then(fn: PhoneAuthSnapshot => void) {
     this._promiseDeferred();
     // $FlowFixMe: Unsure how to annotate `bind` here
     if (this._promise) return this._promise.then.bind(this._promise)(fn);
@@ -338,7 +338,7 @@ export default class PhoneAuthListener {
    * Promise .catch proxy
    * @param fn
    */
-  catch(fn: () => Error) {
+  catch(fn: Error => void) {
     this._promiseDeferred();
     // $FlowFixMe: Unsure how to annotate `bind` here
     if (this._promise) return this._promise.catch.bind(this._promise)(fn);